1. Field of the Invention
The present invention relates to a stitch pattern data processing device for a sewing machine capable of forming a stitch pattern according to stitch pattern data, and more particularly to a stitch pattern data processing device for processing stitch pattern data so as to contract a stitch pattern.
2. Description of the Related Art
Generally, a sewing machine is provided with a stitch forming device including a mechanism for reciprocating a needle and also including a loop taker for forming stitches in cooperation with the needle. A sewing machine is further provided with a material moving device for moving a material to be sewn, e.g., a work fabric, in a direction perpendicular to a reciprocating direction of the needle. The sewing machine is designed to automatically form a stitch pattern on the material to be sewn, by controlling the material moving device according to stitch pattern data in synchronism with the reciprocation of the needle.
In such a sewing machine, some techniques for expanding or contracting a stitch pattern by modifying stitch pattern data are described in Japanese Patent Publication Nos. 61-16193 and 63-14999.
In Japanese Patent Publication No. 61-16193, there is described a technique for increasing the number of stitches upon expansion of the stitch pattern, so as to prevent an excessive space between the adjacent stitches. According to this technique, it is possible to prevent the space between the adjacent stitches from becoming excessive upon expansion of the stitch pattern. However, this technique does not take into consideration that contraction of the stitch pattern can result in the stitches becoming too dense, thus deteriorating the appearance of the contracted stitch pattern.
In Japanese Patent Publication No. 63-14999, there is described a technique for deciding a needle location so as to make substantially constant a stitch pitch of a circular or arcuate stitch pattern irrespective of expansion or contraction of the stitch pattern. This technique, however, can be applied only to a circular or arcuate stitch pattern, and it cannot be applied to a general stitch pattern.